Pulsed time-of-flight laser distance measurement is based on measuring the time it takes for an optical pulse transmitted from a distanced measuring device to travel to a target and reflect from the target back the distance measuring device. Since the velocity of light is known, the measured time can be converted to a distance between the distance measuring device and the target.
When a SPAD (Single Photon Avalanche Detector) is used as a detector of the distance measurement device, the distance measurement suffers from unreliable results in the prior art. Because the SPAD is very sensitive detector, it may be triggered by background illumination or even by thermal noise. The undesired detections due to random triggers result in wrong timings and wrong distances.
There have been attempts to overcome the problems in the prior art by minimizing the background illumination. That is unfortunately not possible for many measurements and that does not solve the problem related to thermal noise, for example. Additionally, the number of measurements have been increased so much that it has been possible to attempt to separate the wrong detections from the correct detections. That, however, lengthens the measurement time substantially and requires an algorithm that should perform the separation reliably. However, a reliable algorithm has not been found. Thus, the measurement becomes complicated but may not provide more reliability.
Hence, there is need for a better performance of detection.